1. Field of the Invention
The invention relates to wireless communications, and more particularly to a cooperative spectrum sensing method and system for locationing primary transmitters in a cognitive radio system.
2. Description of the Related Art
Cognitive radio (CR) aims at improving the spectrum utilization in wireless communications. In a CR system, secondary users, such as customer premise equipments (CPEs), are permitted to utilize vacant spectra in frequency, time and space without causing interference with primary users.
To establish geo-location information of primary users in a CR system, each CPE is required to incorporate a positioning unit, such as a global positioning system (GPS) positioning device, for obtaining GPS information thereof. However, CPEs are likely to be sparsely and randomly distributed in space. In this case, base stations (BSs) of the CR system may use compressive sensing to obtain spectrum sensing signal strengths and locations of the CPEs, thereby reconstructing a power propagation map of the primary users as proposed in an article by E. Candes, J, Romberg, and T. Tao, entitled “Robust Uncertainty Principles: Exact Signal Reconstruction from Highly Incomplete Frequency Information,” IEEE Trans. on Information Theory, No. 2, vol. 52, pp. 489-506, February 2006. Although compressive sensing allows perfect signal reconstruction at a random sampling rate lower than that defined by Nyquist theorem, compressive sensing fails to obtain the number of the primary users when directly applied to spectrum sensing and locationing of the primary users.
Furthermore, a CR system with sparse samples, which has been proposed in an article by Juan Andres Bazerque and Feorgios B. Giannakis, entitled “Distributed Spectrum Sensing for Cognitive Radio Networks by Exploiting Sparsity,” IEEE Trans, on Signal Processing, vol. 58, no. 3, pp. 1847-1862, March 2010, is directed to estimate the locations and power propagation map of primary users. However, since basis weights are estimated, such a CR system cannot ensure accurate location estimation. If the accuracy of location estimation is improved, the amount and complexity of computation will increase, thereby adversely affecting processing speed and protection for the primary users.
Therefore, improvements may be made to the above techniques.